1. Field of the Invention
The present invention relates to electrical switching devices and, more particularly, to an electrical relay utilized to selectively provide electrical power to one or more load devices.
2. Description of Related Art
An electrical relay is an electrically controlled switch used for selectively providing electrical power to one or more load devices. Relays are typically used for controlling a high current (or high voltage) circuit with a low current (or low voltage) signal. A typical electrical relay for selectively providing electrical power to one or more load devices has control terminals for connecting to a control circuit, line terminals for connecting to conductors providing electrical power (i.e., line conductors), and load terminals for connecting to one or more load devices. Load terminals are typically “normally-open” load terminals or “normally-closed” load terminals. Electrical voltage from the line conductors is applied to the normally-closed load terminals when a control signal is absent, and is not applied to the normally-closed load terminals when the control signal is present. The electrical voltage from the line conductors is not applied to the normally-open load terminals when a control signal is absent, and is applied to the normally-open load terminals when the control signal is present.
Relays with both normally-open and normally-closed load terminals are useful in many applications, including heating, ventilating, and air conditioning (HVAC) systems with refrigerant compressors. Compressors typically have crankcase heaters to prevent refrigerant migration and mixing with crankcase oil when the compressor is not running, and to prevent condensation of refrigerant in the crankcase. Crankcase heaters are often not required when the compressor is running, and since they are relatively large electrical loads, it is desirable to turn crankcase heaters off when the compressor is running. A relay with both normally-open and normally-closed load terminals can be used to control a compressor motor and a crankcase heater. With the compressor motor connected to the normally-open load terminals, the compressor motor will operate (i.e., run) only when the control signal is present. With the crankcase heater connected to the normally-closed load terminals, the crankcase heater will operate only when the control signal is absent (i.e., when the compressor motor is not running).
Relays are often used to control loads such as single phase permanent split capacitor (PSC) motors. A typical PSC motor has three leads—two line voltage leads (L1 and L2) and a “Start” lead for connection to a run capacitor. The line voltage leads are typically connected to a relay, and the “Start” lead is connected to one lead of the run capacitor. A second lead of the run capacitor is typically wired to one of the line voltage leads. Even with this relatively simple configuration, there are 120 (five factorial) ways to potentially wire the five leads, only one of which is correct.
A problem arises with relays in that if a wiring error is made when connecting a load device to a load terminal, such as during original assembly, when a faulty load device is replaced, or when a new load device is added, the wiring error may result in injury to a technician performing the work, damage to the relay or to the load device, and/or create an unsafe operating condition.